Functional oxide layers with a variety of compositions have been developed in the art. An example of developed solid state electronic devices with such oxide layers includes ferroelectric thin film-containing devices, which are expected to operate at high speed. BiNbO4 is a Pb-free dielectric material developed for use in solid state electronic devices. BiNbO4 can be formed as an oxide layer by firing at relatively low temperature. As to BiNbO4, there is a report on the dielectric properties of BiNbO4 formed by solid phase growth technique (Non-Patent Document 1). Some patent documents also disclose oxide layers consisting essentially of bismuth (Bi) and niobium (Nb) and having relatively high dielectric constants of 60 or more (up to 180) at 1 kHz (Patent Documents 1 and 2).